Yamaha B-1 restoration/repair

[vintagejapan]

Hi,

First would like to thank all contributing audiokarma members that have helped me and many others bringing back to life all these wonderful vintage pieces that deserve all the TLC they receive.

I am trying to bring back to life a Yamaha B-1 v-fet power amp.
It is in need of one 2SK77 v-fet transistor. Is there other options?
I have seen elsewhere that a 2SK180 from Tokin can be used as a replacement.
Would that be a simple swap or are there further changes in the circuit required.
I have managed to get hold of some 2SK180 and looks like it will fit straight (size-wise)

 

[ryuuoh]

Might be useful for discussion:
http://amp8.com/tr-amp/yamaha/yamb1-82.htm#2sk180

 

[vintagejapan]

Might be useful for discussion:
http://amp8.com/tr-amp/yamaha/yamb1-82.htm#2sk180

Cool thank you ryuuoh,

Thats where I saw these devices for the first time. But the guy mentions that he made some circuit change to accomodate the 2SK180?

 

[Vint Age]

2SK180's ready to rock.

 

[Goldjazz]

I'm also really interested in if there is a replacement for the 2SK77. I'd love to own this amp one day and every one that seems to pop up is in need of service.

Not sure if this is of any use at all but "Digital Do Main" manufactured an amp intended to follow in the footsteps of the B-1. As far as I can tell (6 years ago) they made there own "vertically arranged static induction transistor designed for audio, the 2sk77b" which they use in their amp which they call the B-1a. I have no idea if this can be used in the Yamaha B-1. No idea if they even still exist.

http://www.hi-fiworld.co.uk/amplifiers/47-transistor/112-digital-do-main.html?showall=1

another article on them

http://www.6moons.com/audioreviews/roadtourdigitaldomain/visit.html

I guess you've also seen this thread on the topic

http://www.diyaudio.com/forums/soli...kin-2sj28-2sj18-2sk60-2sj26-2sk76-2sk180.html

 

[vintagejapan]

The B-1 fitted with the K-180' was a success

Just got the amp back a couple of days ago and very happy with the results.
The sound signature is slightly different from original to my ears not the same sweetness on the treble but still unmistakenly V-fet.

Detail overall is more vivid. I will open it up and see at what level my friend biased the 2-SK180's

 

[vonclod]

Good to know, my B1 is a good runner but nice to know all is not lost if the worst happens

 

[Goldjazz]

Awesome, great to hear this has worked. Is there enough info available on how to do this that a experienced tech could carry out the task if I gave them the info?

 

[Vint Age]

The B-1 fitted with the K-180' was a success

Yes it works and very nicely too! Last week I finished successfully installing 4 Tokin 2SK180 V-FET/SIT's in a B-1 that I was recently given to use as a parts donor to help bring another AK'er dead B-1 back to life. That 1 went home to its owner a few month ago who I believe is enjoying listening to it these days... but that's a thread for another day.

The 2SK180's I used are quite different from the original 2SK77 so they're not plug and play drop-ins by any means; to do it right there's some work involved.

Wife and I A/B this B-1 K180 pictured below against our stock B-1 over the course of the day yesterday and we found it to be every bit as engaging and sonically superb as our stock B-1.

This is my forth successful B-1 restore and my first using the 2SK180 as 2SK77 replacements. I was very happy to be able to bring another beautiful B-1 back from the dead!

 

[Mark B]

Hi,

First would like to thank all contributing audiokarma members that have helped me and many others bringing back to life all these wonderful vintage pieces that deserve all the TLC they receive.

I am trying to bring back to life a Yamaha B-1 v-fet power amp.
It is in need of one 2SK77 v-fet transistor. Is there other options?
I have seen elsewhere that a 2SK180 from Tokin can be used as a replacement.
Would that be a simple swap or are there further changes in the circuit required.
I have managed to get hold of some 2SK180 and looks like it will fit straight (size-wise)

The B-1 fitted with the K-180' was a success

Just got the amp back a couple of days ago and very happy with the results.
The sound signature is slightly different from original to my ears not the same sweetness on the treble but still unmistakenly V-fet.

Detail overall is more vivid. I will open it up and see at what level my friend biased the 2-SK180's

That's wonderful, and great news for all B-1 owners.

What did you end up doing with the 3 good 2SK77's?

 

[vintagejapan]

That's wonderful, and great news for all B-1 owners.

What did you end up doing with the 3 good 2SK77's?

They will be kept as spares for my other B-1 fitted with 2SK77's

I will be happy to swap 4 of my 2SK180's plus a single 2SK77 for a good pair of 2SK77's

 

[Mark B]

Yes it works and very nicely too! Last week I finished successfully installing 4 Tokin 2SK180 V-FET/SIT's in a B-1 that I was recently given to use as a parts donor to help bring another AK'er dead B-1 back to life. That 1 went home to its owner a few month ago who I believe is enjoying listening to it these days... but that's a thread for another day.

The 2SK180's I used are quite different from the original 2SK77 so they're not plug and play drop-ins by any means; to do it right there's some work involved.

Wife and I A/B this B-1 K180 pictured below against our stock B-1 over the course of the day yesterday and we found it to be every bit as engaging and sonically superb as our stock B-1.

This is my forth successful B-1 restore and my first using the 2SK180 as 2SK77 replacements. I was very happy to be able to bring another beautiful B-1 back from the dead!

This would make a great thread.

 

[Vint Age]

This would make a great thread.

You've already read it ... and some ...

 

[ilimzn]

Would you care to discus what mods are needed to get the 2SK180 to work? It has quite a LOT of added input capacitance so I expect you did some mods around the gate circuit. The drivers (2SK75) should cope with it...

 

[rottalpha]

 

[Vint Age]

Would you care to discus what mods are needed to get the 2SK180 to work? It has quite a LOT of added input capacitance so I expect you did some mods around the gate circuit. The drivers (2SK75) should cope with it...

Thank you for your interest. I have followed your V-FET comments on this and other forums for several years and I'm looking forward to anything you'd like to add to help keep the B-1 amp working into the future. To my thinking the B-1 is a very unique amp that deserves to be preserved. A working B-1 is far more desirable than a dead one even if it doesn't absolutely meet the original full B-1 specifications.

The higher 2SK180 input capacitance doesn't appear to be an issue for the 2SK75 drivers so no mods were required for that. The amp is stable and working as it should. It sounds superb to my ears albeit they are getting older and perhaps a young set of ears might be able to notice a bit of frequency roll off beyond my hearing range.

The required mods are mostly to adjust for the higher 2SK180 device Mu in order to maintain an equivalent nominal circuit operating current.

One of the more challenging parts of the process is ranking the 2SK180's into usable pairs. For that you need a good sampling of 2SK180's and a curve tracer capable of displaying curves in the region of interest.

 

[ilimzn]

I discovered that a curve tracer is a VERY good thing to have as such, and especially with VFETs.
So, mostly adjusting the bias and balance circuit values to reach the required bias voltages, I suppose.

Yes, the B1 is a unique amp in many ways - topologically, there is nothing similar to it out there, ditto general construction. It was after all a true 'statement amp' right down to semiconductors developed only for use in it. I'd certainly like more of them to work than to turn into parts units.
Once up on a time when Sony 2SK82 were still available, I suppose two in parallel could have been used instead of a single 2SK77, though that requires making a mechanical 'adapter' for the heatsink...

What are your experiences with 2SK75 failing? This is really not easy to replace, especially as Yamaha saw fit to use 3 different 'ranks' in the B1...

 

[Vint Age]

What are your experiences with 2SK75 failing? This is really not easy to replace, especially as Yamaha saw fit to use 3 different 'ranks' in the B1...

I've been very lucky so far that all of the 2SK75s and all of the other small unobtainium FET/V-FETs were still viable in the B1s I've worked on.

 

[rottalpha]

nice work Vintage

 

[Vint Age]

nice work Vintage

Thanks!

I have 4 more usable 2SK180 to get another B-1 working if 1 should find its way to me ...